Phosphor and method for production thereof and plasma display device

ABSTRACT

The present invention relates to a plasma display device apt to increase luminance of a phosphor layer and prevent degradation of a discharge characteristic, and to a phosphor used for the device. This plasma display device has a green phosphor having a crystal structure of Zn 2 SiO 4 :Mn, and a monovalent oxide is substituted for part of the green phosphor. The monovalent oxide is one or more of lithium oxide (Li 2 O), sodium oxide (Na 2 O), potassium oxide (K 2 O), cesium oxide (Cs 2 O), rubidium oxide (Rb 2 O), copper oxide (Cu 2 O), and silver oxide (Ag 2 O). This structure allows reduction of oxygen defects occurring in the green phosphor, suppression of the luminance decrease of the green phosphor, and improvement of a discharge characteristic.

TECHNICAL FIELD

The present invention relates to a plasma display device that is used ina color television receiver or a display for displaying a character oran image and employs a plasma display panel (PDP) using a gas dischargeemission.

BACKGROUND ART

A display device using a plasma display panel (PDP) has recentlyreceived attention as a color display device used for displaying animage in a computer and a television, because this display device usingthe PDP can be large, thin, and light.

The PDP allows full color display by adding and mixing three so calledprimary colors (red, green, and blue). For displaying full colors, thePDP has a phosphor layer for emitting light of each of the three primarycolors, namely red (R), green (G), and blue (B). Phosphor particlesconstituting the phosphor layer are excited by ultraviolet raysgenerated in a discharge cell of the PDP to generate visible light ofeach color.

Compounds employed for the phosphors of respective colors are, forexample, (Y_(1-y),Gd_(y)) BO₃:Eu³⁺ (0≦y≦1) or Y₂O₃:Eu³⁺ for emitting redlight, Zn₂SiO₄:Mn²⁺ for emitting green light, and BaMgAl₁₀O₁₇:Eu²⁺ foremitting blue light. These phosphors are produced by mixingpredetermined raw materials and then by calcining them at a hightemperature of 1000° C. or higher for solid phase reaction (for example,Phosphor Handbook, P219–220, Ohmsha, Ltd.). Phosphor particles producedby this calcination are crushed and classified as red and greenparticles with an average grain size of 2 to 5 μm and blue particleswith an average grain size of 3 to 10 μm and then used.

The crushing and classification of the phosphor particles are performedfor the following reason. In forming the phosphor layer in the PDP, amethod of deforming the phosphor particles of each color to paste andsilk-screening the paste is generally employed. A flatter coated surfacecan thus be easily obtained when grain sizes of the phosphor particlesare smaller and more uniform (uniform grain size distribution). In otherwords, when grain sizes of the phosphor particles are smaller and moreuniform and their shapes are closer to spherical, the coated surface isflatter, filling density of the phosphor particles in the phosphor layerincreases, light emitting surface area of the particles increases,instability in address driving is improved, and hence theoreticalluminance of the PDP can be increased.

When the grain sizes of the phosphor particles are smaller, however, thesurface area of the phosphor particles increases or defects in thesurfaces of the phosphor particles increase. Much hydrocarbon organicgas or water or carbonated gas is therefore apt to adhere to thesurfaces of the phosphor particles. Especially, green phosphor composedof Zn₂SiO₄:Mn has defects (mainly, oxygen defects) in surfaces ofcrystals or in the crystals, and is apt to adsorb hydrocarbon gas orwater existing in the air comparing with blue and red phosphors.Hydrocarbon gas or carbonated gas generated especially in calcining thephosphor is often adsorbed to the green phosphor during or after thecooling process in the calcining. Therefore, disadvantageously, aftersealing the panel, the hydrocarbon gas is released in the panel byelectric discharge and hence reacts with the phosphor or MgO to decreasethe luminance, decrease a driving margin, or increase discharge voltage.

Since the conventional phosphor of Zn₂SiO₄:Mn has many defects near thesurface, the following problem occurs. Specifically, when a phosphorlayer is formed in a method of applying phosphor ink from a nozzle, anorganic binder reacts with the phosphor to clog the nozzle.

The present invention addresses the problems discussed above. Thedefects (mainly, oxygen defects) in the green phosphor are eliminated,thereby suppressing the surface of the green phosphor from adsorbing thehydrocarbon gas or water, suppressing luminance decrease or chromaticitychange of the phosphor, and improving a discharge characteristic.

SUMMARY OF THE INVENTION

The present invention provides a plasma display device having a PDP inwhich a plurality of discharge cells of one color or a plurality ofcolors are arranged, a phosphor layer having a color corresponding tothe color of each discharge cell is disposed, and the phosphor layer isexcited by ultraviolet rays to emit light. The phosphor layer has agreen phosphor having a crystal structure of Zn₂SiO₄:Mn that is excitedby the ultraviolet rays to emit visible light, and a monovalent oxide issubstituted for part of the green phosphor. The monovalent oxide is oneor more of lithium oxide (Li₂O), sodium oxide (Na₂O), potassium oxide(K₂O), cesium oxide (Cs₂O), rubidium oxide (Rb₂O), copper oxide (Cu₂O),and silver oxide (Ag₂O).

This structure allows reduction of oxygen defects occurring in the greenphosphor, suppression of the luminance decrease of the green phosphor,and improvement of a discharge characteristic such as reduction ofaddress discharge failure in driving the plasma display device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a PDP having no front glass substrate inaccordance with an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a structure of an image display regionof the PDP in accordance with the exemplary embodiment.

FIG. 3 is a block diagram of a plasma display device in accordance withthe exemplary embodiment.

FIG. 4 is a sectional view of the structure of the image display regionof the PDP.

FIG. 5 is a schematic block diagram of an ink applying device used informing a phosphor layer in the exemplary embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A phosphor used in a PDP is manufactured in a solid phase reactionmethod or an aqueous solution reaction method, but is apt to generatedefects when grain size of the phosphor is small. Especially in thesolid phase reaction method, it is known that many defects occur whenthe phosphor is calcined and then crushed. It is known that defectsoccur in the phosphor also due to ultraviolet rays with a wavelength of147 nm generated by electric discharge performed in driving a panel (forexample, The Institute, Electronics, Information and CommunicationEngineers, Technology Research Report, EID99–94, Jan. 27, 2000).

Especially, Zn₂SiO₄:Mn as a green phosphor is apt to generate oxygendefects in addition to the defects discussed above because the phosphoris produced by adding excess SiO₂ to ZnO and calcining them at 1100 to1300° C. (Phosphor Handbook, PP 220, 1987, Ohmsha, Ltd.).

We found the following facts. Luminance of the green phosphor is notdecreased only by existence of defects. Hydrocarbon gas and carbonatedgas are adsorbed selectively to the defects (mainly, oxygen defects),and ultraviolet rays or ions are radiated to the adsorbed place to reactthe phosphor with the gases, thereby resulting in luminance decrease andcolor drift. In other words, the oxygen defects near Zn—O and Si—O inthe green phosphor adsorb hydrocarbon gas and carbonated gas, therebyresulting in various degradations. In consideration of these facts, bydecreasing the oxygen defects in the green phosphor, the degradations ofthe green phosphor are prevented in a panel manufacturing process and indriving the panel without decreasing the luminance of the green phosphorin the present invention.

For decreasing the oxygen defects in the green phosphor, a monovalentoxide M₂O (where, M is one or more of Li, Na, K, Rb, Cs, Cu, and Ag) isadded to green phosphor (Zn_(1-x)Mn_(x))₂SiO₄ having a crystal structureof Zn₂SiO₄:Mn, and the monovalent oxide is substituted for a part of thegreen phosphor. As a result, the luminance decrease of the greenphosphor and address discharge failure are intended to be reduced(improvement of the discharge characteristic).

A green phosphor, namely oxide having a crystal structure of Zn₂SiO₄ (Mnis substituted for Zn), generally generates electrons due to oxygendefects and defects by thermal dissociation. In other words, electronshaving a minus charge occur for compensating the plus electrification ofthe oxygen defects. The oxygen defects and electrons are considered torelate to the adsorption of hydrocarbon gas.

Monovalent ions are added to (substituted for) bivalent or quadrivalentions of Zn, Mn, and Si constituting the green phosphor, therebysuppressing the oxygen defects and reducing occurrence of electrons.Therefore, adsorption of hydrocarbon is reduced.

A manufacturing method of the phosphor of the present invention will behereinafter described.

As the manufacturing method of the phosphor body, a solid phase reactionmethod, a liquid phase method, or a liquid spraying method isconsidered. In the solid phase reaction method, conventional oxide orcarbonated raw material is sintered using flux. In the liquid phasemethod, a precursor of a phosphor is formed using a coprecipitationprocess and then thermally treated. Here, in the coprecipitationprocess, organic metallic salt and nitrate are hydrolyzed in aqueoussolution or alkalis or the like is added to them, thereby precipitatingthem. In the liquid spraying method, aqueous solution containing thephosphor material is sprayed into a heated furnace. Even when thephosphor manufactured in any method is used, an effect is obtained byadding monovalent oxide to the phosphor of (Zn_(1-x)Mn_(x))₂SiO₄.

A manufacturing method of a green phosphor by the solid phase reactionmethod is described as an example. Carbonated material or oxide such asZnO, SiO₂, MnCO₃, and M₂O (where, M is one or more of Li, Na, K, Rb, Cs,Cu, and Ag) is used as raw material. The ZnO, SiO₂, and MnCO₃ arefirstly mixed so as to provide a mol ratio corresponding to composition[(Zn_(1-x)Mn_(x))₂SiO₄] of phosphor base material, M₂O is added by 0.001to 0.5 wt % to the [(Zn_(1-x)Mn_(x))₂SiO₄], and the materials arecalcined for 2 hours at 1100 to 1300° C., crushed, and then classified,thereby forming a phosphor.

The liquid phase method of manufacturing a phosphor from aqueoussolution will now be described. Nitrate or organic metallic salt (forexample, alkoxide or acetylacetone) containing elements (Zn, Si, Mn, Li,Na, K, Rb, Cs, Cu, or Ag) constituting a phosphor is firstly dissolvedin water and hydrolyzed to produce precipitate (hydrate). Theprecipitate is crystallized in an autoclave by hydrothermal synthesis,calcined in the air, or sprayed into a high-temperature furnace, therebyproducing a powder body. The powder body is crushed and then calcinedagain for 2 hours, in the air, and at 1100 to 1300° C., therebyproducing a phosphor.

A substituting ratio of monovalent oxide M₂O for (Zn_(1-x)Mn_(x))₂SiO₄is preferably 0.001 to 0.5 wt %. When the substituting ratio is 0.001 wt% or less, the luminance decrease and the address failure cannot beprevented. When the substituting ratio is 0.5 wt % or more, M₂O becomesan impurity to decrease the luminance of the phosphor.

Since monovalent ions are thus substituted for part of Zn, Si, or Mnions in (Zn_(1-x)Mn_(x))₂SiO₄ crystal in the conventional green phosphormanufacturing process, a green phosphor that has no luminance decreaseand is durable against hydrocarbon gas and carbonated gas is obtained.Here, the hydrocarbon gas and carbonated gas have occurred in a phosphorcalcining process, a panel sealing process, a panel aging process, or apanel driving time.

Since substituting monovalent ions decreases defects, when the phosphoris mixed with an organic binder to manufacture phosphor ink, reaction ofthe phosphor and the binder is reduced. Therefore, even when a phosphorlayer is formed in a method of applying this ink from a nozzle, thenozzle is not clogged and a uniform coated film can be obtained.

When grain sizes of the green phosphor particles are small, namely 0.05to 3 μm, the grain size distribution is sufficient, and the phosphorparticles forming the phosphor layer are spherical, the filling densityincreases and light emitting area of the phosphor particlessubstantially contributing to light emission increases. Therefore, theluminance of the PDP increases, and a plasma display device having ahigh luminance characteristic such as suppressed luminance decrease andcolor drift can be obtained.

An average grain size of the phosphor particles is preferably in a rangeof 0.1 to 2.0 μm, and a maximum grain size of the grain sizedistribution is not more than 4 times the average value and a minimumgrain size is not less than ¼ times the average value. Depth to whichultraviolet rays reach in each phosphor particle is short, namely aboutseveral hundreds nm from the surface of the particle, and thesubstantially only surface emits light. When the grain sizes of thephosphor particles are 2.0 μm or less, the surface area of the particlescontributing to light emission increases and the luminous efficiency ofthe phosphor layer is kept high. When the grain sizes are 3.0 μm ormore, the thickness of the phosphor must be 20 μm or more and adischarge space cannot be ensured sufficiently. When the grain sizes are1.0 μm or less, defects are apt to occur and luminance does notincrease.

When the thickness of the phosphor layer is in a range of 8 to 25 timesthe average grain size of the phosphor particles, the luminousefficiency of the phosphor layer is kept high and the discharge spacecan be ensured sufficiently. The luminance of the PDP can be increased.Especially, when the average grain size of the phosphor is 3 μm or less,this effect is large.

The phosphor particles used for the green phosphor layer of the PDP canspecifically be composed of a compound in which (Zn_(1-x)Mn_(x))₂SiO₄ isthe base material and monovalent oxide M₂O (where, M is one or more ofLi, Na, K, Rb, Cs, Cu, and Ag) is substituted by 0.001 to 0.5 wt %. Forincreasing the luminance and preventing the luminance decrease, thevalue of X in this formula preferably satisfies 0.01≦X≦0.2.

The phosphor particles used for a blue phosphor layer can specificallybe composed of a compound represented by the formulaBa_(1-x)MgAl₁₀O₁₇:Eu_(x) or Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x). Forincreasing the luminance, the values of X and Y in this formulapreferably satisfy 0.03≦X≦0.20 and 0.1≦Y≦0.5. The phosphor particlesused for a red phosphor layer can specifically be composed of a compoundrepresented by the formula Y_(2-x)O₃:Eu_(x) or (Y_(1-y),Gd_(y))_(1-x)BO₃:Eu_(x)(0≦y≦1). For increasing the luminance andpreventing the luminance decrease, the value of X in this formulapreferably satisfies 0.05≦X≦0.20.

A manufacturing method of a PDP of the present invention has thefollowing processes:

an applying process of applying, onto a substrate of one panel, pastewhich includes phosphor particles obtained by substituting a monovalentoxide for part of the green phosphor (Zn_(1-x)Mn_(x))₂SiO₄, red and bluephosphor particles, and a binder;

a calcining process of removing the binder contained in the pasteapplied onto the panel; and

a process of overlapping and sealing the panel having the phosphorparticles applied on the substrate in the calcining process and theother panel.

A plasma display device in accordance with an exemplary embodiment ofthe present invention will be described hereinafter with reference tothe accompanying drawings.

FIG. 1 is a schematic plan view of a PDP having no front glasssubstrate, and FIG. 2 is a partially sectioned perspective view of animage display region of the PDP. In FIG. 1, display electrodes, displayscan electrodes, and address electrodes are illustrated, but all of themare not shown for the sake of clarity. A structure of the PDP isdescribed with reference to FIG. 1 and FIG. 2.

In FIG. 1, PDP 100 has front glass substrate (not shown), back glasssubstrate 102, N display electrodes 103, N display scan electrodes 104(the number within the parentheses indicates an ordinal number), Maddress electrodes 107 (the number within the parentheses indicates anordinal number), and airtight seal layer 121 shown by a shaded area.Electrodes 103, 104, 107 constitute an electrode matrix having athree-electrode structure. Cells are formed at intersection points ofdisplay scan electrodes 104 and address electrodes 107. Front glasssubstrate 101 and back glass substrate 102 form discharge space 122 anddisplay region 123.

PDP 100 has a structure in which a front panel and a back panel arebonded together and electric discharge gas is filled into dischargespace 122 formed between the front panel and the back panel. As shown inFIG. 2, the front panel is formed by arranging display electrodes 103,display scan electrodes 104, dielectric glass layer 105, and MgOprotective layer 106 on one main surface of front glass substrate 101.The back panel is formed by arranging address electrodes 107, dielectricglass layer 108, barrier ribs 109, and phosphor layers 110R, 110G, 110Bon one main surface of back glass substrate 102. PDP 100 is coupled toPDP driving device 150 shown in FIG. 3 to constitute the plasma displaydevice.

In driving the plasma display device, as shown in FIG. 3, display drivercircuit 153, display scan driver circuit 154, and address driver circuit155 are firstly coupled to respective electrodes of PDP 100. A voltageis then applied between display scan electrode 104 and address electrode107 in the cell to be lighted in response to control of controller 152,thereby performing the address discharge between them. A pulse voltageis then applied between display electrode 103 and display scan electrode104 to perform the maintenance discharge. This maintenance dischargecauses ultraviolet rays to occur in the cell, and the phosphor layerexcited by the ultraviolet rays emits light, thereby lighting the cell.An image is displayed in combination of lighting and non-lighting ofcells of respective colors.

A manufacturing method of PDP 100 is described.

The front panel is formed by the following procedures. Firstly, Nstripe-like display electrodes 103 and N stripe-like display scanelectrodes 104 (FIG. 2 shows only two pairs of them) are arrangedalternately in parallel on front glass substrate 101. The electrodes arethen covered with dielectric glass layer 105. MgO protective layer 106is then formed on the surface of dielectric glass layer 105. Displayelectrodes 103 and display scan electrodes 104 are made of silver, andformed by applying a silver paste for the electrode by screen printingand then calcining it.

Dielectric glass layer 105 is formed so as to have a predeterminedthickness (about 20 μm) by applying a paste containing lead-base glassmaterial by screen printing and then calcining it at a predeterminedtemperature such as 560° C. for a predetermined period such as 20minutes. As the paste containing lead-base glass material, a mixture ofPbO (70 wt %), B₂O₃ (15 wt %), SiO₂ (10 wt %), Al₂O₃ (5 wt %), and anorganic binder (ethylcellulose of 10% is dissolved in α-terpineol) isused, for example. The organic binder is produced by dissolving resin inorganic solvent. As the resin, acrylic resin may be used instead of theethylcellulose, and as the organic solvent, butylcarbitol may be used.Dispersant such as glycertrioleate may be mixed into the organic binder.

MgO protective layer 106 is made of magnesium oxide (MgO), and formed soas to have a predetermined thickness (about 0.5 μm), for example, in aspattering method or a chemical vapor deposition (CVD) method.

The back panel is formed with M address electrodes 107 arranged inparallel by applying a silver paste for the electrode onto back glasssubstrate 102 by screen printing and then calcining it. Addresselectrodes 107 are coated with a paste containing lead-base glassmaterial by screen printing to form dielectric glass layer 108. The samepaste containing lead-base glass material is repeatedly applied with apredetermined pitch by screen printing and then calcined to form barrierribs 109. Discharge space 122 is partitioned with barrier ribs 109, cell(unit luminous region) by cell, in the line direction.

FIG. 4 is a sectional view of PDP 100. As shown in FIG. 4, interval W ofbarrier ribs 109 is defined as a certain value, for example about 130 to240 μm, in the case of HD-television (TV) of 32-inch to 50-inch.Phosphor layers 110R, 110G, 110B are formed in the following procedures.A groove between barrier ribs 109 is coated with paste-like phosphor inkcomposed of the following components:

red (R) phosphor particles;

blue (B) phosphor particles;

green (G) phosphor particles where monovalent element ions aresubstituted for Zn, Si, and Mn ions in (Zn_(1-x)Mn_(x))₂SiO₄; and

an organic binder.

The phosphor ink is then calcined at 400 to 590° C. to burn down anorganic binder. Thus, respective phosphor particles are bonded to formthe phosphor layers. Thickness L in the laminating direction of each ofphosphor layers 110R, 110G, 110B on address electrode 107 is preferablyabout 8 to 25 times the average grain size of phosphor particles of eachcolor. In other words, for securing a certain luminance (luminousefficiency) in radiating ultraviolet rays to the phosphor layers, eachof phosphor layers 110R, 110G, 110B has a thickness corresponding to 8laminations of the phosphor particles at minimum, preferably about 20laminations, so as to absorb the ultraviolet rays occurring in dischargespace 122 without transmission. When the thickness exceeds the thicknesscorresponding to about 20 laminations, most of the luminous efficiencyof phosphor layers 110R, 110G, 110B saturate and discharge space 122cannot be kept sufficiently large. Phosphor particles produced byhydrothermal synthesis or the like have a sufficiently small grain sizeand a spherical shape. A filling factor of such phosphor layersincreases and the total surface area of the phosphor particles increasescompared with the case of using non-spherical particles even when thenumber of laminations is the same. Therefore, the surface area of thephosphor particles contributing to the actual light emission of thephosphor layers increases and the luminous efficiency also increases. Asynthesis method of phosphor layers 110R, 110G, 110B and a manufacturingmethod of green phosphor particles having substituted monovalent ionsthat are used in the green phosphor layer will be described later.

The front panel and the back panel that are manufactured as describedabove are overlaid so that each electrode of the front panel crosseseach address electrode of the back panel. Glasses for sealing aredisposed at the peripheral edges of the panels, and are calcined, forexample, at about 450° C. for 10 to 20 minutes, thereby forming airtightseal layer 121. The front panel and the back panel are thus sealed andbonded together. The inside of discharge space 122 is temporarilytransferred to a high vacuum state, for example, decompressed to1.1×10⁻⁴ Pa, and then electric discharge gas such as He—Xe-base orNe—Xe-base inert gas is filled into the space at a predeterminedpressure. Thus, PDP 100 is manufactured.

FIG. 5 is a schematic block diagram of ink applying device 200 used informing phosphor layers 110R, 110G, 110B. In FIG. 5, ink applying device200 has server 210, pressure pump 220, and header 230. The phosphor inksupplied from server 210 storing the phosphor ink is pressurized bypressure pump 220 and is supplied to header 230. Header 230 has inkchamber 230 a and nozzle 240, and the phosphor ink pressurized andsupplied to ink chamber 230 a is continuously delivered from nozzle 240.Caliber D of nozzle 240 is preferably 30 μm or more for preventing clogof the nozzle and is not more than interval W (about 130 to 200 μm)between barrier ribs 109 for preventing the ink from squeezing out of agap between the barrier ribs in coating. In other words, the caliber isusually set to 30 to 130 μm.

Header 230 is driven linearly by a header scan mechanism (not shown).Header 230 is driven and phosphor ink 250 is continuously delivered fromnozzle 240, thereby uniformly applying the phosphor ink to a groovebetween barrier ribs 109 on back glass substrate 102. At this time,viscosity of the employed phosphor ink is kept in a range of 1500 to30000 centipoises (CP) at 25° C.

Server 210 has a stirrer (not shown), and the stirring preventsprecipitation of the particles in the phosphor ink. Header 230 isintegrally molded with ink chamber 230 a and nozzle 240, andmanufactured from metallic material by equipment machining and electricdischarge machining.

A forming method of the phosphor layer is not limited to the methoddiscussed above, but various methods such as a photo lithography method,a screen printing method, and a method of placing a film includingphosphor particles can be used.

The phosphor ink is produced by mixing phosphor particles of respectivecolors, a binder, and solvent, and by blending them so as to have aviscosity of 1500 to 30000 CP. A surfactant, silica, or dispersant (0.1to 5 wt %) may be added. As the binder blended into the phosphor ink,ethylcellulose or acrylic resin (0.1 to 10 wt % of the ink) is used. Asthe solvent, α-tapineol or butyl carbitol may be used. Polymer such aspoly methacrylic acid (PMA) or poly vinyl alcohol (PVA) may be used asthe binder, and organic solvent such as diethylene glycol or methylether may be used as the solvent.

As a red phosphor blended into the phosphor ink, a compound representedby formula (Y_(1-y), Gd_(y))_(1-x)BO₃:Eu_(x) (0≦y≦1) or Y_(2-x)O₃:Eu_(x)is used. In this formula, Eu elements are substituted for part of Yelements composing the base material. Substituting ratio X of the Euelements for the Y elements preferably satisfies 0.05≦X≦0.20. When thesubstituting ratio exceeds 0.20, the initial luminance increases but thedecreasing rate of the luminance increases. The compound is thereforedifficult to be employed. When the substituting ratio is less than 0.05,a composition ratio of Eu largely contributing to light emissiondecreases and the luminance decreases. The compound cannot be thereforeused as the phosphor.

As a green phosphor, a compound represented by formula(Zn_(1-x)Mn_(x))₂SiO₄ where monovalent oxide M₂O (where, M is one ormore of Li, Na, K, Rb, Cs, Cu, and Ag) is added by 0.001 to 0.5 wt % isused. In (Zn_(1-x)Mn_(x))₂SiO₄, Mn is substituted for part of Znelements composing the base material. Substituting ratio X of the Mnelements for the Zn elements preferably satisfies 0.01≦X≦0.2.

As a blue phosphor, a compound represented by formulaBa_(1-x)MgAl₁₀O₁₇:Eu_(x) or Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) is used.The Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) and Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) arecompounds where Eu and Sr are substituted for part of respective Bacomposing the base materials. Substituting ratios X and Y of Eu elementsfor Ba elements preferably satisfy 0.03≦X≦0.20 and 0.1≦Y≦0.5, for thereason discussed above.

Phosphor particles used in the present embodiment are produced in thesolid phase reaction method, the aqueous solution method, the sprayingand calcining method, or the hydrothermal synthesis method.

(1) Blue Phosphor

(Ba_(1-x)MgAl₁₀O₁₇:Eu_(x))

In a producing process of a mixture, firstly, barium nitrate Ba(NO₃)₂,magnesium nitrate Mg(NO₃)₂, aluminum nitrate Al(NO₃)₃, and europiumnitrate Eu(NO₃)₃ that are raw materials are mixed at the mole ratio1-X:1:10:X (0.03≦X≦0.25), and they are dissolved into an aqueous medium,thereby producing the mixture. As the aqueous medium, ion-exchangedwater and pure water are preferable because they have no impurities.However, they may contain non-aqueous solvent (methanol or ethanol).

The hydrated mixture is then injected into a vessel made of gold orplatinum having corrosion resistance or heat resistance. The hydratedmixture is then hydro-thermally synthesized in a high pressure vesselusing the following apparatus, in 12 to 20 hours, at a predeterminedtemperature (100 to 300° C.), and at a predetermined pressure (0.2 to 10MPa). The apparatus is, for example, an autoclave allowing simultaneouspressurizing and heating.

The produced powder is calcined in a reducing atmosphere containinghydrogen by 5% and nitrogen by 95% for example, at a predeterminedtemperature such as 1350° C., for a predetermined period such as 2hours. The calcined powder is classified to provide the desired bluephosphor Ba_(1-x)MgAl₁₀O₁₇:Eu_(x).

The phosphor particles produced by the hydrothermal synthesis have aspherical shape and an average grain size of about 0.05 to 2.0 μm,namely smaller than that of phosphor particles produced by theconventional solid phase reaction. Here, “spherical” is defined suchthat most phosphor particles have an axial diameter ratio (shorter axialdiameter/longer axial diameter) of 0.9 to 1.0, for example. All phosphorparticles need not be in this range.

The blue phosphor can be produced by a spraying method of spraying thehydrated mixture from a nozzle into a high-temperature furnace tosynthesize a phosphor without injecting the hydrated mixture into thevessel made of gold or platinum.

(Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x))

This blue phosphor is different from the blue phosphor ofBa_(1-x)MgAl₁₀O₁₇:Eu_(x) only in raw material, and is produced in thesolid phase reaction method. The employed raw material is described.

Barium hydroxide Ba(OH)₃, strontium hydroxide Sr(OH)₂, magnesiumhydroxide Mg(OH)₂, aluminum hydroxide Al(OH)₂, and europium hydroxideEu(OH)₂, that are raw materials are weighed so as to provide anappropriate mole ratio. They are mixed together with AlF₃ used as flux,and calcined for 12 to 20 hours at a predetermined temperature (1300 to1400° C.), thereby producing Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) wherequadrivalent ions are substituted for Mg and Al. An average grain sizeof the phosphor particles obtained in the present method is about 0.1 to3.0 μm.

The phosphor particles are calcined in a reducing atmosphere containinghydrogen by 5% and nitrogen by 95% for example, for 2 hours, and at apredetermined temperature (1000 to 1600° C.), and then are classifiedwith an air classifier. Thus, phosphor powder is provided.

Oxide, nitrate, and hydroxide have been mainly used as raw materials ofthe phosphor. However, organometallic compounds containing elements suchas Ba, Sr, Mg, Al, and Eu, for example metal alkoxide and acetylacetone,may be used.

(2) Green Phosphor

[(Zn_(1-x)Mn_(x))₂SiO₄]

Zinc Nitrate Zn(NO₃)₂, silicon nitrate Si(NO₃)₄, and manganese nitrateMn(NO₃)₂ that are raw materials are firstly mixed at the mole ratio1-X:1:X (0.01≦X≦0.20) to produce a mixture. Monovalent oxide M₂O (where,M is one or more of Li, Na, K, Rb, Cs, Cu, and Ag) is then mixed intothe mixture by 0.001 to 0.5 wt % to (Zn_(1-x)Mn_(x))₂SiO₄, again. Theproduced mixture is calcined for 2 hours at a temperature of 1000 to1300° C., and then crushed and classified, thereby producing greenphosphor particles having a grain size of 0.1 to 3 μm.

When a green phosphor is produced in the hydrothermal synthesis method,zinc nitrate Zn(NO₃)₂, silicon nitrate Si(NO₃)₄, and manganese nitrateMn(NO₃)₂ that are raw materials are firstly mixed at the mole ratio1-X:12:X (0.01≦X≦0.10) and dissolved into ion-exchanged water to producea mixture. Hydrated solution of monovalent oxide M₂O (where, M is one ormore of Li, Na, K, Rb, Cs, Cu, and Ag) is then produced, and added tothe mixture by 0.001 to 0.5 wt % of the phosphor.

In a hydration process, then, a basic aqueous solution such as ammoniaaqueous solution is dropped into the mixture to produce hydrate. In ahydrothermal synthesis process, the hydrate and ion-exchanged water arethen injected into a capsule made of platinum or gold having corrosionresistance or heat resistance, and then hydro-thermally synthesized in ahigh pressure vessel such as an autoclave, at a predeterminedtemperature such as 100 to 300° C., at a predetermined pressure such as0.2 to 10 MPa, and for a predetermined period such as 2 to 20 hours.

The hydro-thermally synthesized product is dried to produce(Zn_(1-x)Mn_(x))₂SiO₄ mixed with desired monovalent oxide. Thanks to thehydrothermal synthesis process, the produced phosphor particles have agrain size of about 0.1 to 2.0 μm and a spherical shape. The phosphorparticles are then annealed in the air at 800 to 1300° C., and thenclassified to provide a green phosphor.

(3) Red Phosphor

[(Y, Gd)_(1-x)BO₃:Eu_(x)]

In a producing process of a mixture, yttrium nitride Y(NO₃)₃, gadoliniumnitrate Gd(NO₃)₃, boric acid H₃BO₃, and europium nitride Eu(NO₃)₃ thatare raw materials are mixed at the mole ratio 1-X:2:X (0.05≦X≦0.20) (theratio of Y to Gd is 65 to 35). They are then thermally treated in theair for 2 hours at 1200 to 1350° C., and then classified, therebyproviding a red phosphor.

[Y_(2-x)O₃:Eu_(x)]

In a producing process of a mixture, yttrium nitrate Y(NO₃)₃ andeuropium nitrate Eu(NO₃)₃ that are raw materials are mixed at the moleratio 2-X:X (0.05≦X≦0.30), and dissolved into ion-exchanged water toproduce a mixture.

In a hydration process, then, a basic aqueous solution such as ammoniaaqueous solution is added to the mixture to produce hydrate.

In a hydrothermal synthesis process, the hydrate and ion-exchanged waterare then injected into a vessel made of platinum or gold havingcorrosion resistance or heat resistance, and then hydro-thermallysynthesized in a high pressure vessel such as an autoclave, at atemperature of 100 to 300° C., at a pressure of 0.2 to 10 MPa, for 3 to20 hours. The produced compound is then dried to produce desiredY_(2-x)O₃:Eu_(x). The phosphor is then annealed in the air for 2 hoursat 1300 to 1400° C., and then classified to provide a red phosphor.Thanks to the hydrothermal synthesis process, the produced phosphorparticles have a grain size of about 0.1 to 2.0 μm and a sphericalshape. These grain size and shape are suitable for forming a phosphorlayer having a high luminance characteristic.

The conventional phosphor is used in the red and blue phosphor layers ofthe PDP discussed above. A phosphor composed of (Zn_(1-x)Mn_(x))₂SiO₄for which oxide having monovalent elements is substituted is used in thegreen phosphor layer. A conventional green phosphor is largely apt todegrade due to hydrocarbon gas and water in each process comparing withthe green phosphor of the present invention, so that luminance of theconventional green phosphor is apt to decrease in emitting green light.When the green phosphor of the present invention is used, luminance ofthe green cells increases, degradation in the panel manufacturingprocess is suppressed, and therefore color drift and address dischargefailure are prevented. Therefore, when the green phosphor of the presentinvention is used, luminance in displaying white can be increased, andphosphor ink can be applied to the inside of the barrier ribs withoutclogging even with a thin nozzle.

For evaluating performance of the plasma display device of the presentinvention, samples in accordance the present embodiment weremanufactured and performance evaluation tests on the sample were made.Test results are analyzed.

In each manufactured plasma display device, the size of the device is42-inch (HD-TV specification with a rib pitch of 150 μm), thickness ofthe dielectric glass layer is 20 μm, thickness of the MgO protectivelayer is 0.5 μm, and distance between each display electrode and eachdisplay scan electrode is 0.08 mm. Discharge gas is gas in which xenongas is mixed by 5% into neon as a main component, and is filled into thedischarge space at a predetermined discharge gas pressure.

As a green phosphor used in the PDP of each of the samples 1 to 10, aphosphor in which monovalent oxide is partially substituted for(Zn_(1-x)Mn_(x))₂SiO₄ is used. Respective synthesis conditions are shownin Table 1.

TABLE 1 Green Phosphor (Zn_(1−x)Mn_(x))₂SiO₄ Kinds and ratios SampleManufacturing of substituted Manufacturing Manufacturing No Amount ofEu_(x) method monovalent oxide Amount of Eu_(x) method Amount of Mn_(x)method Red Phosphor Blue Phosphor (Y,Gd)_(1−x)BO₃: Eu_(x)Ba_(1−x)MgAl₁₀O₁₇: Eu_(x)  1 x = 0.01 Solid-phase Li₂O 0.01% x = 0.1Solid-phase x = 0.03 Hydrothermal reaction method reaction methodsynthesis method  2 x = 0.05 Solid-phase Na₂O 0.01% x = 0.2 Solid-phasex = 0.05 Hydrothermal reaction method reaction method synthesis method 3 x = 0.1 Solid-phase K₂O 0.1% x = 0.3 Solid-phase x = 0.1 Hydrothermalreaction method reaction method synthesis method  4 x = 0.2 Solid-phaseRb₂O 0.2% x = 0.15 Solid-phase x = 0.2 Hydrothermal reaction methodreaction method synthesis method Red Phosphor Blue Phosphor(Y_(1−x))₂O₃: Eu_(x) Ba_(1−x−y)Al₁₀O₁₇: Eu_(x)  5 x = 0.03 Solid-phaseCs₂O 0.1% x = 0.01 Hydrothermal x = 0.01 y = 0.1 Solid-phase reactionmethod synthesis method reaction method  6 x = 0.1 Hydrothermal Cu₂O0.05% x = 0.1 Hydrothermal x = 0.1 y = 0.3 Solid-phase synthesis methodsynthesis method reaction method  7 x = 0.1 Hydrothermal Ag₂O 0.05% x =0.15 Aqueous solution x = 0.1 y = 0.5 Solid-phase synthesis methodmethod reaction method  8 x = 0.2 Solid-phase Li₂O 0.01% x = 0.2Solid-phase x = 0.2 y = 0.3 Solid-phase reaction method reaction methodreaction method  9 x = 0.2 Solid-phase Li₂O 0.2% x = 0.2 Solid-phase x =0.2 y = 0.3 Solid-phase reaction method reaction method reaction method10 x = 0.1 Solid-phase Li₂O 0.5% x = 0.15 Solid-phase x = 0.1 y = 0.5Solid-phase reaction method reaction method reaction method  11* x = 0.1Solid-phase No substituted x = 0.15 Solid-phase x = 0.1 y = 0.5Solid-phase reaction method monovalent oxide reaction method reactionmethod *Sample No. 11 shows comparative example

In samples 1 to 4, (Zn_(1-x)Mn_(x))₂SiO₄ is used as the green phosphor,(Y, Gd)_(1-x)BO₃:Eu_(x) is used as the red phosphor,Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) is used as the blue phosphor, and they arecombined. Table 1 shows synthesizing methods of the phosphors,substituting ratios of Mn and Eu largely contributing to the lightemission, and substituting ratios (wt %) of monovalent oxide for(Zn_(1-x)Mn_(x))₂SiO₄ and their types for the green phosphor. Here,substituting ratios of Mn and Eu mean substituting ratios of Mn for Znand substituting ratios of Eu for Y or Ba.

In samples 5 to 10, Y_(2-x)O₃:Eu_(x) is used as the red phosphor,(Zn_(1-x)Mn_(x))₂SiO₄ is used as the green phosphor,Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) is used as the blue phosphor, and theyare combined. Table 1, similarly to the samples 1 to 4, shows methodsand conditions for synthesizing of the phosphors, and substitutingratios of monovalent oxide for (Zn_(1-x)Mn_(x))₂SiO₄ and their types forthe green phosphor.

Each phosphor ink used for forming each phosphor layer is produced bymixing each phosphor including the phosphor particles shown in Table 1,resin, solvent, and a dispersant.

Viscosity (25° C.) of each phosphor ink is measured to be kept in therange of 1500 to 30000 CP. It is found from the observation of thephosphor layer that wall surfaces of barrier ribs in the formed phosphorlayer are uniformly coated with the phosphor ink.

Caliber of a nozzle used for the coating at this time is 100 μm. Anaverage grain size of the phosphor particles used in the phosphor layeris 0.1 to 3.0 μm, and the maximum grain size is 8 μm or less.

In sample 11, as the green phosphor particles, conventional phosphorparticles in which substitution of monovalent oxide is not especiallyperformed are used.

(Test 1)

Formed samples 1 to 10 and reference sample 11 are tested with respectto change of luminance of the green phosphor in the phosphor calciningprocess (520° C., 20 minutes) in the back panel manufacturing process,and a change rate of the phosphor of each color from the beginning tothe finishing of the calcination is measured. In other words, theluminance of powder is measured before the calcination, and theluminance is measured after the application and the calcination of thepaste.

(Test 2)

A change (decrease) rate of the luminance of the green phosphor from thebeginning to the finishing of the panel bonding process (sealing process450° C., 20 minutes) is measured in the panel manufacturing process.

(Test 3)

Change rates of luminance decreases are measured when a panel is lightedto display white on the entire screen and to display green. In thismeasurement, discharge maintaining pulses with a voltage of 200 V and afrequency of 50 kHz are applied to the plasma display devicecontinuously for 200 hours, the panel luminances are measured before andafter the application, and each change rate of luminance is calculatedbased on the measurement. The change rate of luminance is represented bythe expression, ((luminance after the application−luminance before theapplication)/luminance before the application)×100.

The address failure in address discharge is determined depending on theexistence of flicker of an image. When flicker occurs even at one place,the address failure is determined to occur. The luminance distributionof the panel is determined by measuring luminances of white displayed onthe entire screen with a luminance meter.

(Test 4)

It is evaluated whether or not nozzle clogging occurs when greenphosphor ink is applied continuously for 100 hours using a nozzle with acaliber of 100 μm.

Table 2 shows results of the luminances, luminance change rates, and thenozzle clogging in tests 1 to 4.

As shown in Table 2, reference sample 11 in which monovalent oxide isnot substituted for (Zn_(1-x)Mn_(x))₂SiO₄ as the green phosphor has ahigh decrease rate of luminance of green light in each process.Especially, the decrease rates of sample 11 are −4.1% in the phosphorcalcining process and −13.2% in the sealing process, but those ofsamples 1 to 10 are lower values such as −0.2 to −0.5%, and −1.8 to−2.3%. In an acceleration life test of 200 V and 50 kHz, change rates indisplaying white on the entire screen are −20.5% in sample 11 and −3.0to −3.8% in samples 1 to 10. The change rates of luminance of greenlight are −15.6% in sample 11, but −1.8 to −2.4% in samples 1 to 10. Insamples 1 to 10, no address failure occurs.

That is because the substitution of monovalent oxide for(Zn_(1-x)Mn_(x))₂SiO₄ as the green phosphor largely reduces oxygendefects in the green phosphor, especially oxygen defects near Zn—O andSi—O. The reduction of the oxygen defects is caused by the fact thathydrocarbon gas or water is not adsorbed to the defects (the oxygendefects near Zn—O and Si—O) in the surface of the phosphor. Here, thehydrocarbon gas or water exists in atmosphere in calcining the phosphor,or occurs from MgO, the barrier ribs, the sealing flit material, and thephosphor

(Test 5)

A phosphor in which monovalent oxide is not substituted for(Zn_(1-x)Mn_(x))₂SiO₄ as the green phosphor is left in the atmospherefor 100 minutes, and then analyzed by a temperature desorption gas massspectroscopic (TDS) analysis. As a result, the peak (near 100 to 400°C.) of adsorption of hydrocarbon gas in this case is 10 times higherthan those in samples 1 to 10 having the added monovalent oxide.

TABLE 2 States of Luminance decrease rate clogging after Luminancedecrease rate Luminance decrease rate (%) of phosphor after Presence orgreen ink is (%) of phosphor firing (%) of phosphor when application ofdischarge absence of continuously (520° C.) in back panel panels areseald(450° C.) susutain pulses address faillure applied from Samplemanufacturing process in panel sealing process (200 V, 100 KHz, 100hours) in address nozzle for No. Green Green White on entire screenGreen discharge 100 hours 1 −0.5 −2.0 −3.3 −2.4 Absence No clogging 2−0.4 −2.1 −3.2 −2.2 Absence No clogging 3 −0.3 −2 −3.4 −2.5 Absence Noclogging 4 −0.5 −1.9 −3.1 −2 Absence No clogging 5 −0.5 −1.8 −3.3 −2.1Absence No clogging 6 −0.4 −2 −3.6 −2.1 Absence No clogging 7 −0.3 −2.1−3.7 −2.5 Absence No clogging 8 −0.2 −2.2 −3.3 −2.3 Absence No clogging9 −0.3 −1.8 −3.8 −2.4 Absence No clogging 10  −0.2 −2.3 −3 −1.8 AbsenceNo clogging 11* −4.1 −13.2 −20.5 −15.6 Presence Clogging in 4 hours*Sample No. 11 shows comparative example

INDUSTRIAL APPLICABILITY

The present invention provides a plasma display device having a phosphorlayer of a color corresponding to the color of each discharge cell. Thephosphor layer has a green phosphor having a crystal structure ofZn₂SiO₄:Mn that is excited by ultraviolet rays to emit visible light,and monovalent oxide is substituted for part of the green phosphor. Themonovalent oxide is one or more of lithium oxide (Li₂O), sodium oxide(Na₂O), potassium oxide (K₂O), cesium oxide (Cs₂O), rubidium oxide(Rb₂O), copper oxide (Cu₂₀), and silver oxide (Ag₂O).

This structure allows reduction of oxygen defects occurring in the greenphosphor, suppression of the luminance decrease of the green phosphor,and improvement of a discharge characteristic such as reduction ofaddress discharge failure in driving the plasma display device.

1. A plasma display device comprising: a plasma display panel having aplurality of discharge cells of at least one color and a phosphor layerof a color corresponding to the color of each of said discharge cells;wherein a phosphor constituting said phosphor layer is operable to beexcited by an ultraviolet ray so as to emit light; wherein said phosphorlayer comprises a green phosphor layer; and wherein said green phosphorlayer includes a phosphor in which at least one monovalent oxide of agroup including potassium oxide (K₂O), cesium oxide (Cs₂O), rubidiumoxide (Rb₂O), copper oxide (Cu₂O), and silver oxide (Ag₂O) is added to agreen phosphor (Zn_(1-x)Mn_(x))₂SiO₄ (0.01≦x≦0.2) having a crystalstructure of Zn₂SiO₄:Mn in an amount in a range of 0.001 wt % to 0.5 wt%.
 2. A phosphor for displaying images in a plasma display device, saidphosphor comprising: a green phosphor to be incorporated into the plasmadisplay device said green phosphor having a crystal structure ofZn₂SiO₄:Mn, wherein said green phosphor is operable to be excited by anultraviolet ray so as to emit visible light, wherein at least onemonovalent oxide of a group including potassium oxide (K₂O), cesiumoxide (Cs₂O), rubidium oxide (Rb₂O), copper oxide (Cu₂O), and silveroxide (Ag₂O) is added to the green phosphor (Zn_(1-x)Mn_(x))₂SiO₄(0.01≦x≦0.2) in an amount in a range of 0.001 wt % to 0.5 wt %.
 3. Amethod of manufacturing a green phosphor for use in a plasma displaydevice, the green phosphor having a crystal structure of Zn₂SiO₄:Mn andbeing operable to be excited by an ultraviolet ray so as to emit visiblelight, said method comprising: producing a hydrate coprecipitate bydissolving in water an organic metallic salt or a nitrate containingelements (Zn, Si, and Mn) composing the green phosphor and elements (Rb,Cs, Cu, and Ag) composing a monovalent oxide so that a substitutingratio of a monovalent oxide M₂O (where M is one of K, Rb, Cs, Cu, andAg) for the green phosphor (Zn_(1-x)Mn_(x))₂SiO₄ (0.01≦x≦0.2) is in arange of 0.001 wt % to 0.5 wt %; calcining the hydrate coprecipitate inair; and producing the green phosphor having a crystal structure ofZn₂SiO₄:Mn by again calcining the hydrate coprecipitate at a temperaturein a range of 1100 to 1300° C.
 4. A method of manufacturing a greenphosphor for use in a plasma display device, the green phosphor having acrystal structure of Zn₂SiO₄:Mn and being operable to be excited by anultraviolet ray so as to emit visible light, said method comprising:producing a hydrate coprecipitate by dissolving in water an organicmetallic salt or a nitrate containing elements (Zn, Si, and Mn)composing the green phosphor and elements (Rb, Cs, Cu, and Ag) composinga monovalent oxide so that the substituting ratio of a monovalent oxideM₂O (where M is one of K, Rb, Cs, Cu, and Ag) for the green phosphor(Zn_(1-x)Mn_(x))₂SiO₄ (0.01≦x≦0.2) is in a range of 0.001 wt % to 0.5 wt%; crystallizing the hydrate coprecipitate in an autoclave; andproducing the green phosphor by calcining the hydrate coprecipitate at atemperature in a range of 1100 to 1300° C.